Additive manufacturing (AM) processes, such as Direct Laser Metal Fusion (DMLF), have recently come to prominence as a cost-effective alternative to traditional manufacturing techniques. However, external and internal (e.g., hollow or cored) surfaces of articles formed by AM can exhibit surface roughness associated with the application of successive layers or the unintended clinging of powder particles to the free edges, as shown in FIG. 1. Internal defects and surface connected defects, like those shown in FIG. 2, may render a component unusable.
Prevention of this roughness condition may not be critical if the surface can be subsequently improved in a cost-effective manner. To the extent that such mechanical surface roughness is non-conforming with the engineering design intent or for cosmetic reasons, a means of smoothing the surface (or controlled excess stock removal) is desired, especially those surfaces which are inaccessible to hand-finishing or machine-finishing methods. Additionally, justification for required surface improvement, encapsulation, and subsequent hot isostatic press (HIP) processing extends to various metallurgical reasons including 1) smoothing undesirable surface roughness, 2) smoothing roughness to enable subsequent encapsulation of surface connected porosity and defects for HIP processing to eliminate internal and surface defects in the AM component, 3) removal of metallurgical surface defects such as micro cracking, and 4) being able to predicatively remove excess stock or non-conforming layers without creating metallurgical issues.
U.S. Pat. No. 8,506,836 discloses surface finish and encapsulation technologies for nickel-based alloys, but to date no such technology has ever been developed for aluminum alloys. For aluminum alloys, mechanical or electro-polish smoothing of external surfaces may reduce roughness, as shown in FIG. 3, but they may not enable surface connected defects to be eliminated in HIP processing. Thus, encapsulation is required to bridge the surface defects to enable successful HIP processing. U.S. Pat. Nos. 2,654,701 and 3,993,238 disclose zincate plating for aluminum, but they do not disclose diffusing the zinc into the substrate followed by subsequent stripping to enhance surface finish and enable successful encapsulation.
Accordingly, there remains a need in the art for surface improvement of additively manufactured articles produced with aluminum alloys. Furthermore, other desirable features and characteristics of the disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.